In automatic lathes of the type in question, a stock bar which is just being machined and which is held and guided in the associated stock bar feeding apparatus concentrically to the axis of rotation of the operating workpiece spindle of the automatic lathe, has, up to now, been advanced each time following the machining or rather production of a workpiece either by means of an advancing apparatus associated with the automatic lathe or by means of a stock bar slide of the bar loading magazine. Such an advancing apparatus is located between the bar loading magazine and the workpiece clamping location of the workpiece spindle of the automatic lathe, wherein this clamping location is arranged at the front end of the workpiece spindle facing the working area of the automatic lathe and is customarily designed as a so-called clamping chuck. The advancing apparatus is normally an advancing claw similar to a chuck which is arranged in the workpiece spindle behind the workpiece chuck of this spindle. On the other hand, the stock bar slide of a bar loading magazine is an advancing element which abuts against the rear end of the stock bar which is just being machined and is still guided in the bar loading magazine and pushes this bar forwards in the direction towards the workpiece spindle of the automatic lathe. In both cases, the stock bar is, of course, always advanced when the chuck of the workpiece spindle of the automatic lathe is open.
In connection with an automatically operating bar loading magazine the feeding apparatuses first mentioned result in certain advantages in comparison with stock bar slides: The construction of the stock bar magazine becomes simpler because the stock bar slide with its drive can be omitted, the constructional length of the stock bar magazine becomes smaller, and it is easier to adapt the diameter of the guide means of the bar loading magazine guiding the stock bar just being machined to stock bars of different diameters because no stock bar slide is present.
The present invention relates exclusively to stock bar feeding apparatuses for such machine tools which have their own stock bar advancing apparatus available or with which a stock bar advancing apparatus arranged between the actual machine tool and the actual bar loading magazine is associated.
DE-PS 1 777 170 describes a bar loading magazine which is combined with a single spindle lathe, in the workpiece spindle of which an advancing apparatus with an advancing claw is arranged behind the chuck holding a workpiece to be machined. The bar loading magazine has a guiding and receiving box arranged on a frame for receiving and guiding a new stock bar which is to be fed to the lathe and this box is formed by an upper and a lower receiving channel respectively shaped like half shells in cross section. These channels leave a longitudinal slot free between them which is penetrated by a pushing-in entrainer which is secured to a drive chain extending, like the receiving box, in the direction of the axis of rotation of the workpiece spindle and can be placed against the rear end of a new stock bar to be fed to the lathe in order to press this through the advancing claw of the workpiece spindle--such advancing claws are customarily spring claws which are not tensioned and opened but abut against the stock bar only due to their spring action. The upper receiving channel of the receiving box is borne by a pivotable lever in order to be able to open a guide passage of the receiving box formed by the two receiving channels and allow a new stock bar to roll out of a slide bearing a supply of stock bars into the lower receiving channel.
As is customary in lathes combined with a bar loading magazine, a new stock bar is advanced by the pushing-in entrainer through the advancing claw and the open workpiece chuck of the workpiece spindle to such an extent that it projects somewhat beyond the front end of the workpiece spindle and reaches the area of a lathe tool designed as a so-called cut-off chisel, with which the front, rough end of the new stock bar is faced once the chuck of the workpiece spindle has been clamped and the latter caused to rotate together with a new stock bar.
This known construction has various disadvantages: Since the two receiving channels form between them an open longitudinal slot for the passage of the pushing-in entrainer, the stability of the guide passage is impaired by this longitudinal slot; moreover, in the case of a bar loading magazine with a guide passage flooded with oil, the slot interrupts the hydrodynamic lubricating and guiding or rather centering effect. The machining of stock bars which were, originally, already of unequal lengths requires a measuring device (also called a push-in control) which sees to it that when a new stock bar is inserted into the workpiece spindle of the lathe the stock bar reaches as far as the cut-off chisel of the lathe so that the front end of the bar can be faced; for this purpose, a stop is provided, which is moved in between bar loading magazine and workpiece spindle of the lathe and moved forward against the front end of the new stock bar, as well as, in addition, a control chain which can be switched in via a magnetic coupling and predetermines the push-in path of the new stock bar as far as the cut-off chisel once the stop has been withdrawn. Since the push-in force which is necessary to press the new stock bar through the advancing claw of the workpiece spindle is considerable, and since it is, in addition, not allowable for the new stock bar to travel against the movable stop with such a high feeding force, an adjustable slipping clutch must be provided in the drive of the pushing-in entrainer. Since a new stock bar to be fed to the lathe is, from the beginning, pushed from behind by the pushing-in entrainer, the receiving box formed by the two receiving channels must have the length of the longest stock bar to be machined in order to prevent any buckling of the stock bar under the influence of the push-in force (as soon as a new stock bar has been pushed into the workpiece spindle of the lathe, a guide passage shorter by the length of the workpiece spindle and, therefore, a receiving box shorter by this length would, on the other hand, be adequate).
The object underlying the invention was to create for a machine tool, in particular an automatic lathe, which has its own advancing apparatus available for the section-wise advancing of a stock bar to be machined in the machine tool or which has such an advancing apparatus associated with it, a stock bar feeding apparatus which does not have the disadvantages connected with the insertion of a new stock bar into the machine tool by means of a pushing-in element to be placed against the rear end of the stock bar.